I am installing a 12"x24" ceramic tile in my kitchen. We have 7/8" thick, t&g 8"w wood planks on a diagonal, installed above 10x2 floor joists (16"o.c.). What should I install over the top of the wood planks to ensure rigidity of the floor? 1/2" osb glued and screwed? 1/4" cement backerboard glued and screwed? Or a system like the schluter ditra mortared down? I want to make sure that this floor lasts. Thank you so much!

12-17-2012, 05:46 PM

SouthernCanuck

Re: Tile Substrate

My vote is for the ditra. Not knowing the length and width of the room I won't guess as to the deflection rate.

Post this query on the John Bridge tiling forum. That is where you will get the definitive answer as well as the handy dandy deflection calculator.

12-17-2012, 05:53 PM

Scott Sidler

Re: Tile Substrate

SouthernCanuck is right about the John Bridge forum for the best tile answers.

I've had good luck using 1/4" cement board thinset and screwed into the T&G subfloor then painting 2 coats of Redgard over the whole thing. The Redgard adds a water barrier and also with 2 coats it creates an anti crack membrane. Also, since you are tiling in a wood framed house always use crack-prevention mortar. I find that the combo of those steps has kept my tile jobs from cracking because the extra precautions gives the floor plenty of flexibility to move with the house.

I haven't tried the ditra yet, but I'm anxious to soon.

12-17-2012, 06:47 PM

HoustonRemodeler

Re: Tile Substrate

The John Bridge Tile Forum has a handy dandy deflecto-meter you can use to see if your joists are suitable for tiling.

Over such plank floors the minimum plywood is 1/2" CC or better installed properly (read the plywood thread in the JBF library)

Ditra / CBU / greenskin can all be applied over plywood according to manufacturers instructions.

Tell the guys over at the JB Forum we sent you and we want our mascot back.

12-17-2012, 08:44 PM

nlbauser

Re: Tile Substrate

Thank you for your comments!
Based on further research, here is what seems to make sense:
1. Screw the plank sub floor to the joists on every board, at every joist.
2. Lay new 1/2" plywood down. According to the other website, I need to be 4" away from the joists with the short ends (16" OC joists).
3. Screw the 1/2" ply down every 6" on edge, 8" in the field.
4. Lay Ditra according to instructions and tile over it.

12-17-2012, 10:37 PM

HoustonRemodeler

Re: Tile Substrate

2- When installing plywood over planking, Ignore the planking and screw the new plywood to the joists as if the planking weren't there.